Many places where you would sail into will not allow firearms. It is a complicated situation. In some ports, you need to declare any weapons onboard and let them hang onto them while you are in their country. You can get them back on the way out. If you try to hide them, they will find them. Customs agents are accustomed to searching for drugs on board. They will seize your boat and put you in jail if they find undeclared firearms.
Other places will seize them and keep them no matter what.
You need a long range firearm. Shotgun is only good when they’re trying to board or after have gotten on board. Go for a large capacity auto-loader with high powered round. Think AR-10 chambered in .308, or similar.
You need to be able to damage a vessel from a ways off. Of course these guys are willing to fire RPG’s at naval ships, so you might be better off steering well clear of dangerous areas.
You’ve got the right idea, but a .50 Cal sniper rifle is better for stand off protection, but will get you arrested and jailed in most ports! Best to just stay away ‘til the USA gets some cojones!!
JC